Minimum requirements
PHP 7.1
MyBB 1.8.0
PluginLibrary
664 chmod permissions on inc/functions_user.php and global.php

Features
Modern chat feeling
Messages are displayed in a modern fashion, inspired by WhatsApp's design. Own messages are displayed on the right side while others' messages are placed on the left in a different color. Folders are hidden and give way to a single page with all active conversations, all in one place.

Easy read status
Messages sent have a little double check icon which turns blue when the recipient reads the message. This allows for quick visualization of a message read status, and replaces de facto the old tracking page.

Smooth integration
Symposium is compatible with most of other plugins as long as they use the native MyBB pm class, which is often if not always the case. This is possible because Symposium does not run separately from the native PM system, but integrates within it and enhances it while keeping its structure and functions intact. Some examples? MyAlerts, PM on registration, Newpoints, Flyover 2.4, BankPipe beta 11... they are all working out of the box.

Converter with backwards compatibility
Symposium automatically sorts and converts existing private messages into conversations upon install. When you uninstall the plugin, your messages will still be there, except if you have deleted them when Symposium was installed.

WARNING SIGN If you did not have copies of sent messages in your "Sent" folder before Symposium was installed, conversations will just include the other user's messages and will look like a monologue. Messages sent from when Symposium has been installed onwards will have hard copies in the "Sent" folder by default.

Mass deleting
Deleting PMs has always been painful and limited, due to many PMs belonging to the same person. Symposium boosts messages deletion by allowing users to delete multiple, entire conversations and/or messages at once.

WARNING SIGN If you enable the "Move to trash" setting, PMs will be moved to the Trash bin folder instead of being deleted permanently. However, they will not be displayed, as Symposium does not (yet) feature a Trash folder.

CALENDAR since messages sent are hard copied into the sender's "Sent" folder, in future releases you will be able to set a timespan during which an user can delete messages for him and the recipient(s), after which he can only delete his own messages.

Editor support
Symposium replicates the default editor settings by using the codebuttons template, exactly like in posts. Plugins which hook into or use this template are also supported (eg.: Rin Editor). The editor is loaded both in the new conversation page and in quick replies.

Group chat support
Symposium allows group chats. Users can send the same message to several recipients at once, whom will see the message within the same conversation.

Installation
Upload the files maintaining the same folder structure as they come in the package and click the button Install & activate within your board's plugin list.

Convert existing private messages
Symposium can convert existing private messages to conversations. The process does not alter existing private messages but it adds columns and tables in the database, so you will be able to go back anytime by uninstalling Symposium.

WARNING SIGN Before starting the conversion, ensure your /cache folder has 777 chmod permissions.

In the plugins list under Symposium's row you will notice a text saying you have a certain number of PMs to convert. Start the conversion by clicking on the homonym button. The process will be performed incrementally and progress will be displayed in real time.

WARNING SIGN Do not close the page before the conversion is over.

Templates and stylesheets
Symposium adds a CSS file named symposium.css to every theme of your board, and several templates with the symposium_ prefix. You can customize the plugin's appearance by editing the stylesheet's CSS rules and templates.

Full credits to Shade at MyBB Boost